In his day, Finn, a hairy mongrel and former Belfast stray, was a daredevil. He would leap spread-eagled into huge waves at the seaside and launch himself off 10-feet-high banks during river walks.

Soon after I got him in early 1998, I thought our brief relationship was over when he leapt over a harbour wall at Howth. I ran over, my heart in my mouth, expecting the worst. There he was, perched on a rock having landed cleanly, looking just a little sheepish.

A favourite trick of ours was me throwing a tennis ball close to the top of some rapids. Finn would swim towards the ball, grasp it in his jaws and then be swept down the rapids, emerging sodden and triumphant on the other side.

Toby and Finn leave Washington DC for London in 2005. Finn used to travel quite happily in a crate in the cargo holdAlas, such antics are long gone. Now, Finn, who used to be able to run like the wind, is so arthritic he has to be carried up and down stairs. Sometimes we find him splayed on the hardwood floor unable to get up.

Although he still enjoys his walks – two a day – he is so slow and deaf and blind that I often have to retrace my steps to find him and point him back in the right direction. He is given four pills twice a day and will occasionally yelp from the pain in his limbs. Massaging them seems to soothe him.

His teeth, for many years almost perfect, are now rotten and he can’t eat biscuits as he used to. His breath smells like a sewer.

Back in 2001, Finn was more than capable of getting a bit of speed up, even on dry land

I first met Finn when looking for a pet at the National Canine Defence League home outside Ballymena in Northern Ireland where I was working as a newspaper reporter. Then, he was called Buddy and listed as a ‘terrier cross, reference number 34/98’. All the other dogs were barking and flinging themselves at the sides of their cages. Finn was quiet, just looking up at me and wagging his tail.

His look seemed to say: ‘OK, it’s a deal - you and me going through life together.’ When I got him home, it was clear he’d never really been touched by people before. But within days, he was curling up next to me. The kennel I had bought for him went unused – Finn made it clear he was sleeping on my bed.

He soon became minutely attuned to my moods. I remember returning to Belfast after more than a week away covering the Omagh bomb in 1998. After picking Finn up from friends, I sat down on the sofa in silence.

Finn in 2007: 'OK, it's a deal - you and me going through life together'

It was the first time I had been able to reflect properly on the horror of what had happened and the carnage that had killed 29 people. Tears welled up. Then I felt Finn’s head resting gently on my thigh; he had sensed my sadness and was looking up at me with those soulful, consoling brown eyes.

In the 14-plus years since then, Finn has lived the life of a foreign correspondent’s dog. I took him with me to Washington where, coming from the UK, he suffered no quarantine restrictions.

For him, the major ramification of September 11th was more vigilant security guards and, therefore, an end to visits to my office block in Washington. After the Iraq invasion, we both headed to Jerusalem. Perhaps the sounds of the bombs exploding reminded him of his birthplace.

Finn was always a survivor. When I had to leave him home alone all day in Washington, he would sit in the window looking sad. Eventually, a Belgian lady called Martine who lived a few doors away took pity on him and asked if she could walk him each lunchtime.

In Jerusalem, he learned to accept that not everyone loved dogs. We had a regular five-mile running route close to the old Green Line, Israel’s pre-1967 border, that could prove hazardous. On one run, he was attacked by a feral cat and then had to dodge stones thrown by Palestinian youths.

There were also problems with ultra-orthodox Jews, who tend to consider dogs unclean animals. One religious woman went into spasms of horror when Finn trotted past her as I walked him on the lead. His less-than-helpful contribution was to try to lick her leg.

During these years, Finn was the one constant in my life. When I was jailed for two weeks in Zimbabwe, accused of breaking immigration rules in the country where foreign journalists are banned, the way I’d get to sleep on a hard floor in a cell filled with more than 100 inmates was to close my eyes and imagine I was stroking Finn’s silky coat.

Knowing he was there back home was something that helped sustain and soothe me when I was away. I used to have frequent nightmares about Iraq – of being kidnapped by men with long beards and threatened with beheading.

Once, one ended with me looking down from the clouds at Finn running happily through lush green Irish fields. It seemed that I was dead. When I woke, I was at first disturbed. But there was a serenity about the image that was comforting. From then on, the nightmares receded.

Right from the outset, Finn was happy each day just to do what I was doing. Until recently, he never had much of a routine. When I went away, he always embraced being looked after by others - staying with families, couples, single friends with cats, even an old lady in her 80s with a fondness for her drinks trolley who looked after two dozen dogs at a time.

There has always been a Finn fan club of people willing to take him in. In 14 years, he’s never had to go to a boarding kennels.

Each time I left him somewhere, by the time I was walking out of the door, he was already sitting happily at the feet of the latest surrogate owner. He’d fended for himself as a stray; he always knew how to get by. Air travel, in a crate in the hold, was never a problem for him.

In 2007, I was a family dog: Toby with his wife Cheryl, daughter Tessa and Finn, whose life changed when wife and children came along

As a bachelor’s dog, Finn was a fine wing man. A female guest in the house always brought the best out in him. After Finn had wagged his tail, rolled on his back and nuzzled against her, she would invariably exclaim: ‘I think he really likes me!’

Finn’s life, along with mine, changed in 2006 when I got married. We moved back to Washington and he began sleeping on the floor, not the bed. He immediately accepted Cheryl as a co-owner.

A year after we were married, I was away when Cheryl suffered an early miscarriage. Finn knew something was very wrong and throughout that awful night he never left her side.

Happily, in 2007 Finn witnessed a small bundle being brought back from the hospital - our baby daughter Tessa. I’ll never forget his ears pricking up when he first heard her cry.

From day one, Finn would sleep beside Tessa’s crib. When she began to walk, she and Finn would play games in which they would wrestle a toy duck off each other. Sometimes we would catch Tessa chewing one of Finn’s old bones. Perhaps it helped her build up antibodies.

When Miles came along three years ago, Finn decided his new sleeping spot was right outside their bedrooms – or inside one of them if a door was left open. He had become a faithful guardian to our children. Sometimes, they would pull his tail, grab clumps of his hair or try to ride him like a horse. But Finn never snapped or bit.

Finn can’t play much with the children any more. They hug him and lie beside him to talk to or kiss him. They realise he is too old to do much. He chased his last squirrel quite some time ago. When he’s gone, the kids say, we’ll get a new puppy, or perhaps a hamster.

Throughout his life, whenever I’ve been home Finn has almost always been in the same room as me during the daytime. That’s still the case. If he wants to come up or go down stairs, he barks so I can carry him. He’s never minded being picked up and at about 35lbs I can lift him with one arm.

He won’t eat his pills if they’re put in his food but he’ll let me put my hand in his mouth and place them in his throat.

Finn’s decline has been slow and steady. He knows his limitations and seems to sense he is in his final days. Occasionally, however, he still wags his tail.

Every few days or so he’ll briefly break into a trot and try to chase a stick. He stills rubs his face on the sofa and snorts – an expression of happiness. We recently took him for a beach holiday in North Carolina, where he happily padded around in the surf.

Tessa hugs Finn during a family holiday in North Carolina, where the dog played happily on the beach last month

Finn follows Miles along the beach in North Carolina

Up until recently, Finn has seemed like the dog he once was, just older. But there are some signs of dementia now. The other day, he was stuck in a corner of our bedroom, whimpering and apparently unsure where he was.

The most difficult decision will be when to accept Finn is at the end of the line.

When that happens, a vet who has been kind to him will come to our house to give him that final, lethal injection. I don’t want his last minutes alive to be spent slipping and scrambling on a metal table while smelling the disinfectant of the animal hospital.

I have a hunch that a lot of people put their pets down prematurely. We don’t want to do that. On the other hand, it would be wrong to keep him alive if he’s just miserable.

Finn’s always been intuitive rather than intelligent (he never worked out that the way to get a big stick through an opening was to turn his head so it was diagonal). I have a feeling he will somehow let me know when he feels it’s time to go.

Perhaps strangely, I don’t feel sad that Finn will soon have to leave us, though I dread the moment the decision will have to be made. He’s been a wonderful companion and had quite a life. That will be something I will always celebrate.